Hereditary hemochromatosis, a disease characterized by excess iron absorption leading to diabetes, cardiomyopathy, cirrhosis, and arthropathies, is arguably the most common clinically important genetic disorder of Europeans. Recently an HLA Class 1 gene, HLA-H was implicated in the etiology of this disease. Over 80 percent of hemochromatosis patients are homozygous for a C282Y mutation. Compound heterozygotes for C282Y and H62D appear to have an increased incidence of the disease. Sixty-thousand adults undergoing health care screening in the Kaiser-Permanente system will be screened, determining serum iron, iron binding capacity, ferritin, and mutations in HLA-H. Patients classified as having hemochromatosis will be phlebotomized to remove excess iron and to measure iron stores. This will establish the relationship between genotype, age, sex and clinical state, and size of iron stores, and provide data that can be used to guide programs screening for hemochromatosis. The hypotheses that heterozygotes are more susceptible to cardiovascular disease and other disorders and that they are benefited by being less susceptible to iron deficiency anemia will be tested using the extensive Kaiser-Permanente database. Hemochromatosis mutations, other than those known, will be sought. The HLA-H gene product may function like other HLA class 1 genes, binding peptides and associating with proteins such as beta2 microglobulin, calreticulin, transporter associated with antigen processing (TAP) and tapascin. Alternatively, it may function as a signaling molecule, like the Fc receptor. Determining how the HLA-H gene product functions should provide insight into its role in maintaining iron homeostasis. This will be done by using immunoprecipitating HLA-H containing complexes, determining HLA-H Fc receptor signaling properties and measuring the binding of peptides and other small molecules by HLA-H.